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Re: Making an X-10 lamp module immune to dimming



In article <XOOdnWtOoK-abdXVnZ2dnUVZ_jidnZ2d@xxxxxxx>, ROBERT_GREEN1963@xxxxxxxxx (Robert Green) writes:

| You're correct.  At first glance I thought he was talking about putting a
| solid state relay inside an appliance module to eliminate the clack.  After
| your comment, I went and tested the modules I have and while the wall
| switches respond to All Lights ON/OFF, the lamp modules don't.  They only
| respond to All Lights ON.

Although All Lights Off was part of the original command set it was not
implemented by X10 until pretty late in the game.  I don't think most of
my cheap wall switches respond to it either.  The relay wall switches have
responded to it for a long time, though; possibly since their introduction.

| Bummer.  Well, that makes the project somewhat
| less attractive.  At least the All Lights ON command is more useful to me
| than All Lights Off would be.  How is that the X-10 security system flashes
| the house lights?

It alternates All Lights On with All Units Off.

| My whole premise
| was based on a misunderstanding of how triacs work.  I thought they were
| merely high speed electronic relays.

They are to a first approximation, but there are a lot of details that
can trip you up.

| It's become apparent that the triac can only do its magic when synched to
| the zero crossing.

You can turn a triac on any time, but unless you are dimming it is usually
best to turn it on near a zero crossing.  You can't turn it off unless
there is no current flowing.

| Perhaps you could be kind enough to explain what would happen if the line to
| the triac gate was high all the time.  Would it conduct only on the first
| half cycle, or not at all or would the magic smoke escape?  (-:

Having the gate "high" is probably not the best way to think of it.  A
triac is triggered by current flowing between gate and MT1.  There are
two possible directions for that current and two possible polarities for
the voltage between MT1 and MT2.  Together this gives you four combinations
which are commonly referred to as quadrants of operation.  (If you google
the terms you will find pictures.)  Most garden variety triacs can be
triggered in any quadrant; however, it may require more current to trigger
in some quadrants than in others.  Some triacs are designed to be triggerable
in only three of the four quadrants to reduce certain kinds of false
retriggering.  There may be more exotic variations.

Note that the requirement for the trigger current to flow between gate and
MT1 is independent of the quadrants.  I've read claims that some triacs
are symmetrical with respect to MT1 and MT2 but I wouldn't want to count
on it.

So, assuming you have satisfied the triggering polarity requirements (if
any) and you drive current between the gate and MT1 all the time, the
triac will conduct all the time.

				Dan Lanciani
				ddl@danlan.*com


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